It’s an article of faith that innovation is vital to San Diego County’s economic future, but I always like to see for myself.

In San Marcos, a 50-year-old innovation from technology giant General Atomics is paying dividends for relatively tiny Avista Technologies Inc.

G.A. invented a type of filter in the early 1960s that uses a physical process called reverse osmosis to remove salt and other molecules from seawater to make clean drinking water. The company sold the technology in 1974.

Although it doesn’t get the press of other local innovations like biotech and wireless communications, that invention spawned the world’s leading cluster of desalination companies in San Diego.

Avista was founded 13 years ago in a local library by three North County entrepreneurs looking to fill a niche making eco-friendly chemicals to improve the performance of reverse osmosis and other water purification systems.

Now the company has 38 employees and is outgrowing its 14,000-square-foot headquarters and research center in a tidy San Marcos industrial park.

As I toured their plant early this month, CEO Dave Walker described how the company’s patented products help customers keep filter membranes clean, long-lasting and more energy efficient.

If they’ve heard of reverse osmosis at all, most people associate the technology with large-scale desalination like the project Poseidon Water is building in Carlsbad to tap the Pacific Ocean for drinking water.

Avista has also built a business in the much larger global market for industrial water filtration. The company helps purify water for Jack Daniel’s whiskey, Crest toothpaste and Intel’s microchip fabricating lines.

The company ships products to North and South America and Europe, with manufacturing in Los Angeles and Great Britain. Walker’s next project is expansion into Asia.

This kind of innovation-driven business, which pulls dollars from outside the region, forms a competitive advantage worth protecting, says Mark Cafferty, CEO of the San Diego Regional Economic Development Corp.

Using 2011 data, EDC estimates that 67.4 percent of the regional economy is inherently local. Examples range from restaurants to real estate.

Sometimes, local projects boost the traded categories. Take Poseidon’s desal plant, a hotly contested infrastructure project that took years to get regulatory approval.

Using a standard methodology, an economist at M.Cubed in Oakland estimated in 2011 that building the Poseidon project will create 2,586 jobs over its 32-month construction schedule.

Most of these are specialized, highly skilled construction and fabrication jobs. And its direct construction cost of $400 million or so will create a nearly $1 billion splash as it ripples through the state economy.

Setting aside the very real benefits of securing water supplies for biotech and other vital technologies, the Poseidon project will boost the local desalination cluster.

Just the desalination piece of the worldwide purification market represented $10 billion in 2010 and is projected to grow to $30 billion by 2016, according to a report last year by the San Diego Maritime Industry Alliance.